For the reasons I pointed out in the other thread, I think Norine makes even somewhat more sense than Danelle, who we saw the last time six books ago. Norine had contact with Egwene and Leane in KoD. It makes sense that Mesaana wanted to observe those two. Furthermore, it makes sense that Mesaana would choose the White Ajah, since it is the smallest (thus less danger to often meet other AS) and the philosophy fits her character. Plus, as the White Norine, Mesaana had better opportunities to observe Alviarin. The reason why Alviarin still didn't realize in the beginning of KoD that Norine must be Mesaana (maybe both look and sound a bit alike), are probably that she has SH'S orders and Silviana's punishments on her mind. Maybe Alviarin figured out Mesaana's alter ego somewhere in KoD off-screen, though.

If RJ wants Mesaana to be an AS, Norine seems like the best bet!